1. Field of the Invention
This invention relates generally to a manual service disconnect (MSD) device for electrically disconnecting a high voltage battery in an electric vehicle and, more particularly, to a manual service disconnect device for electrically disconnecting a high voltage battery in an electric vehicle, where the manual service disconnect device also provides a pre-charge function.
2. Discussion of the Related Art
The automotive industry is now experiencing a significant increase in the number of vehicles that provide some fraction of their propulsion via high voltage electrical systems. These vehicles include hybrid vehicles, such as the extended range electric vehicles (EREV) that combine a battery and a main power source, such as an internal combustion engine, fuel cell systems, etc., and electric only vehicles, such as the battery electric vehicles (BEV). All of these types of electric vehicles employ a high voltage battery that includes a number of battery cells. These batteries can be different battery types, such as lithium ion, nickel metal hydride, lead acid, etc. The battery can include individual battery modules where each battery module may include a certain number of battery cells, such as twelve cells. The individual battery cells may be electrically coupled in series, or a series of cells may be electrically coupled in parallel, where a number of cells in the module are connected in series and each module is electrically coupled to the other modules in parallel. Different vehicle designs include different battery designs that employ various trade-offs and advantages for a particular application.
In order to comply with federal requirements for high voltage safety, and for other tactical reasons, many of these types of vehicles use electrical contactors (relays) to confine high voltage to the vehicle's energy storage system (ESS) during shut-down periods and under some fault conditions, such as vehicle impacts. Particularly, the high voltage battery in an electric vehicle is selectively coupled to the vehicle's high voltage bus by battery contactors. When the vehicle is shut off, the contactors are opened and the battery is disconnected from the high voltage bus. When the vehicle is switched on, the contactors are closed and the battery voltage is coupled to the high voltage bus.
Several other high voltage components are electrically coupled to the high voltage bus, including a traction motor power inverter module (TPIM) that converts the DC high voltage bus signal to an AC signal suitable for the AC propulsion motors on the vehicle. The TPIM and other modules and circuits coupled to the high voltage bus generally include a relatively large capacitor, sometimes referred to as an X-capacitor, coupled across the positive and negative lines of the high voltage bus that filters bus voltage noise that may otherwise have a degrading effect on the performance of the module. However, as the battery contactors are being closed and the battery voltage is coupled to the high voltage bus lines, these capacitors act as a direct short across the bus lines until the capacitor has had an opportunity to charge, which is generally only a few milli-seconds. This limited time direct short has a degrading effect on many of the electrical components in the system as a result of the high voltage, including the capacitor itself and the contactors, which limits their life.
In order to eliminate or reduce this current spike from the direct short at system start-up, it is known to provide a pre-charge resistor in the battery circuit that operates as a load to limit the current while the several capacitors are being charged. In other words, the pre-charge resistor pre-charges the vehicle's high voltage bus prior to closing the main bus contactors during vehicle start-up in order to avoid high in-rush current spikes that may otherwise damage the high voltage capacitors. In one particular design, a negative battery contactor is closed at start-up and the pre-charge resistor is coupled across the positive bus contactor, which remains open until the pre-charge function is completed.
It is known in the art to provide a manual service disconnect (MSD) device in the vehicle battery circuit, which is a device that electrically disconnects and separates a high voltage battery into two parts. Service personnel can remove the MSD device when servicing the electric vehicle to reduce the possibility of coming in contact with the full high voltage of the battery. Also, the MSD device can be opened or removed by first responders after the vehicle is involved in a collision or other significant event, where the high voltage system may potentially be compromised.
The primary reason for using a contactor to perform the pre-charge function is that with current technology, it is sometimes preferable to discharge the X-capacitors after the vehicle's drive cycle is completed. In the future, however, high voltage components will presumably have less parasitic current draw and will therefore be more energy efficient to maintain the X-capacitors charged between drive cycles. Furthermore, vehicles of the future are much more likely to be connected to the power grid when they are not being driven, further reducing the likelihood that it will be required to frequently discharge the X-capacitors. Because of this, it is likely that the pre-charge function for future vehicles will need to be performed significantly less often.